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<div class="title">samples/cpp/demhist.cpp</div>  </div>
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<p>An example for creating histograms of an image</p>
<div class="fragment"><div class="line"><span class="preprocessor">#include &quot;<a class="code" href="../../d1/d4e/utility_8hpp.html">opencv2/core/utility.hpp</a>&quot;</span></div><div class="line"><span class="preprocessor">#include &quot;<a class="code" href="../../d1/d4f/imgproc_2include_2opencv2_2imgproc_8hpp.html">opencv2/imgproc.hpp</a>&quot;</span></div><div class="line"><span class="preprocessor">#include &quot;<a class="code" href="../../d6/d87/imgcodecs_8hpp.html">opencv2/imgcodecs.hpp</a>&quot;</span></div><div class="line"><span class="preprocessor">#include &quot;<a class="code" href="../../d4/dd5/highgui_8hpp.html">opencv2/highgui.hpp</a>&quot;</span></div><div class="line"></div><div class="line"><span class="preprocessor">#include &lt;iostream&gt;</span></div><div class="line"></div><div class="line"><span class="keyword">using namespace </span><a class="code" href="../../d2/d75/namespacecv.html">cv</a>;</div><div class="line"><span class="keyword">using namespace </span><a class="code" href="../../d8/dcc/namespacestd.html">std</a>;</div><div class="line"></div><div class="line"><span class="keywordtype">int</span> _brightness = 100;</div><div class="line"><span class="keywordtype">int</span> _contrast = 100;</div><div class="line"></div><div class="line"><a name="_a0"></a><a class="code" href="../../d3/d63/classcv_1_1Mat.html">Mat</a> image;</div><div class="line"></div><div class="line"><span class="comment">/* brightness/contrast callback function */</span></div><div class="line"><span class="keyword">static</span> <span class="keywordtype">void</span> updateBrightnessContrast( <span class="keywordtype">int</span> <span class="comment">/*arg*/</span>, <span class="keywordtype">void</span>* )</div><div class="line">{</div><div class="line">    <span class="keywordtype">int</span> histSize = 64;</div><div class="line">    <span class="keywordtype">int</span> brightness = _brightness - 100;</div><div class="line">    <span class="keywordtype">int</span> contrast = _contrast - 100;</div><div class="line"></div><div class="line">    <span class="comment">/*</span></div><div class="line"><span class="comment">     * The algorithm is by Werner D. Streidt</span></div><div class="line"><span class="comment">     * (http://visca.com/ffactory/archives/5-99/msg00021.html)</span></div><div class="line"><span class="comment">     */</span></div><div class="line">    <span class="keywordtype">double</span> a, b;</div><div class="line">    <span class="keywordflow">if</span>( contrast &gt; 0 )</div><div class="line">    {</div><div class="line">        <span class="keywordtype">double</span> delta = 127.*contrast/100;</div><div class="line">        a = 255./(255. - delta*2);</div><div class="line">        b = a*(brightness - delta);</div><div class="line">    }</div><div class="line">    <span class="keywordflow">else</span></div><div class="line">    {</div><div class="line">        <span class="keywordtype">double</span> delta = -128.*contrast/100;</div><div class="line">        a = (256.-delta*2)/255.;</div><div class="line">        b = a*brightness + delta;</div><div class="line">    }</div><div class="line"></div><div class="line">    <a class="code" href="../../d3/d63/classcv_1_1Mat.html">Mat</a> dst, hist;</div><div class="line">    image.<a name="a1"></a><a class="code" href="../../d3/d63/classcv_1_1Mat.html#adf88c60c5b4980e05bb556080916978b">convertTo</a>(dst, <a name="a2"></a><a class="code" href="../../d1/d1b/group__core__hal__interface.html#ga32b18d904ee2b1731a9416a8eef67d06">CV_8U</a>, a, b);</div><div class="line">    <a name="a3"></a><a class="code" href="../../d7/dfc/group__highgui.html#ga453d42fe4cb60e5723281a89973ee563">imshow</a>(<span class="stringliteral">&quot;image&quot;</span>, dst);</div><div class="line"></div><div class="line">    <a name="a4"></a><a class="code" href="../../d6/dc7/group__imgproc__hist.html#ga4b2b5fd75503ff9e6844cc4dcdaed35d">calcHist</a>(&amp;dst, 1, 0, <a class="code" href="../../d3/d63/classcv_1_1Mat.html">Mat</a>(), hist, 1, &amp;histSize, 0);</div><div class="line">    <a class="code" href="../../d3/d63/classcv_1_1Mat.html">Mat</a> histImage = <a name="a5"></a><a class="code" href="../../d3/d63/classcv_1_1Mat.html#a69ae0402d116fc9c71908d8508dc2f09">Mat::ones</a>(200, 320, <a class="code" href="../../d1/d1b/group__core__hal__interface.html#ga32b18d904ee2b1731a9416a8eef67d06">CV_8U</a>)*255;</div><div class="line"></div><div class="line">    <a name="a6"></a><a class="code" href="../../dc/d84/group__core__basic.html#ga1b6a396a456c8b6c6e4afd8591560d80">normalize</a>(hist, hist, 0, histImage.<a name="a7"></a><a class="code" href="../../d3/d63/classcv_1_1Mat.html#abed816466c45234254d25bc59c31245e">rows</a>, <a name="a8"></a><a class="code" href="../../d2/de8/group__core__array.html#ggad12cefbcb5291cf958a85b4b67b6149fa9f0c1c342a18114d47b516a88e29822e">NORM_MINMAX</a>, <a name="a9"></a><a class="code" href="../../d1/d1b/group__core__hal__interface.html#ga4a3def5d72b74bed31f5f8ab7676099c">CV_32F</a>);</div><div class="line"></div><div class="line">    histImage = <a name="a10"></a><a class="code" href="../../d1/da0/classcv_1_1Scalar__.html#ac1509a4b8454fe7fe29db069e13a2e6f">Scalar::all</a>(255);</div><div class="line">    <span class="keywordtype">int</span> binW = <a name="a11"></a><a class="code" href="../../db/de0/group__core__utils.html#ga085eca238176984a0b72df2818598d85">cvRound</a>((<span class="keywordtype">double</span>)histImage.<a name="a12"></a><a class="code" href="../../d3/d63/classcv_1_1Mat.html#aa3e5a47585c9ef6a0842556739155e3e">cols</a>/histSize);</div><div class="line"></div><div class="line">    <span class="keywordflow">for</span>( <span class="keywordtype">int</span> i = 0; i &lt; histSize; i++ )</div><div class="line">        <a name="a13"></a><a class="code" href="../../d6/d6e/group__imgproc__draw.html#ga07d2f74cadcf8e305e810ce8eed13bc9">rectangle</a>( histImage, <a name="a14"></a><a class="code" href="../../dc/d84/group__core__basic.html#ga1e83eafb2d26b3c93f09e8338bcab192">Point</a>(i*binW, histImage.<a class="code" href="../../d3/d63/classcv_1_1Mat.html#abed816466c45234254d25bc59c31245e">rows</a>),</div><div class="line">                   <a name="_a15"></a><a class="code" href="../../db/d4e/classcv_1_1Point__.html">Point</a>((i+1)*binW, histImage.<a class="code" href="../../d3/d63/classcv_1_1Mat.html#abed816466c45234254d25bc59c31245e">rows</a> - <a class="code" href="../../db/de0/group__core__utils.html#ga085eca238176984a0b72df2818598d85">cvRound</a>(hist.<a name="a16"></a><a class="code" href="../../d3/d63/classcv_1_1Mat.html#aa5d20fc86d41d59e4d71ae93daee9726">at</a>&lt;<span class="keywordtype">float</span>&gt;(i))),</div><div class="line">                   <a class="code" href="../../d1/da0/classcv_1_1Scalar__.html#ac1509a4b8454fe7fe29db069e13a2e6f">Scalar::all</a>(0), -1, 8, 0 );</div><div class="line">    <a class="code" href="../../d7/dfc/group__highgui.html#ga453d42fe4cb60e5723281a89973ee563">imshow</a>(<span class="stringliteral">&quot;histogram&quot;</span>, histImage);</div><div class="line">}</div><div class="line"></div><div class="line"><span class="keyword">const</span> <span class="keywordtype">char</span>* keys =</div><div class="line">{</div><div class="line">    <span class="stringliteral">&quot;{help h||}{@image|baboon.jpg|input image file}&quot;</span></div><div class="line">};</div><div class="line"></div><div class="line"><span class="keywordtype">int</span> main( <span class="keywordtype">int</span> argc, <span class="keyword">const</span> <span class="keywordtype">char</span>** argv )</div><div class="line">{</div><div class="line">    <a name="_a17"></a><a class="code" href="../../d0/d2e/classcv_1_1CommandLineParser.html">CommandLineParser</a> parser(argc, argv, keys);</div><div class="line">    parser.<a name="a18"></a><a class="code" href="../../d0/d2e/classcv_1_1CommandLineParser.html#a2e11e779047efded23f75d9c5c5dd82e">about</a>(<span class="stringliteral">&quot;\nThis program demonstrates the use of calcHist() -- histogram creation.\n&quot;</span>);</div><div class="line">    <span class="keywordflow">if</span> (parser.<a name="a19"></a><a class="code" href="../../d0/d2e/classcv_1_1CommandLineParser.html#a8c41cf242b2ad8c0472e3b57893ef200">has</a>(<span class="stringliteral">&quot;help&quot;</span>))</div><div class="line">    {</div><div class="line">        parser.<a name="a20"></a><a class="code" href="../../d0/d2e/classcv_1_1CommandLineParser.html#a84cda3794b765332bfe43bf8367222fb">printMessage</a>();</div><div class="line">        <span class="keywordflow">return</span> 0;</div><div class="line">    }</div><div class="line">    <span class="keywordtype">string</span> inputImage = parser.<a name="a21"></a><a class="code" href="../../d0/d2e/classcv_1_1CommandLineParser.html#a190215863579a6d244dccfd261ee0224">get</a>&lt;<span class="keywordtype">string</span>&gt;(0);</div><div class="line"></div><div class="line">    <span class="comment">// Load the source image. HighGUI use.</span></div><div class="line">    image = <a name="a22"></a><a class="code" href="../../d4/da8/group__imgcodecs.html#ga288b8b3da0892bd651fce07b3bbd3a56">imread</a>(<a name="a23"></a><a class="code" href="../../d6/dba/group__core__utils__samples.html#ga3a33b00033b46c698ff6340d95569c13">samples::findFile</a>(inputImage), <a name="a24"></a><a class="code" href="../../d8/d6a/group__imgcodecs__flags.html#gga61d9b0126a3e57d9277ac48327799c80ae29981cfc153d3b0cef5c0daeedd2125">IMREAD_GRAYSCALE</a>);</div><div class="line">    <span class="keywordflow">if</span>(image.empty())</div><div class="line">    {</div><div class="line">        std::cerr &lt;&lt; <span class="stringliteral">&quot;Cannot read image file: &quot;</span> &lt;&lt; inputImage &lt;&lt; std::endl;</div><div class="line">        <span class="keywordflow">return</span> -1;</div><div class="line">    }</div><div class="line"></div><div class="line">    <a name="a25"></a><a class="code" href="../../d7/dfc/group__highgui.html#ga5afdf8410934fd099df85c75b2e0888b">namedWindow</a>(<span class="stringliteral">&quot;image&quot;</span>, 0);</div><div class="line">    <a class="code" href="../../d7/dfc/group__highgui.html#ga5afdf8410934fd099df85c75b2e0888b">namedWindow</a>(<span class="stringliteral">&quot;histogram&quot;</span>, 0);</div><div class="line"></div><div class="line">    <a name="a26"></a><a class="code" href="../../d7/dfc/group__highgui.html#gaf78d2155d30b728fc413803745b67a9b">createTrackbar</a>(<span class="stringliteral">&quot;brightness&quot;</span>, <span class="stringliteral">&quot;image&quot;</span>, &amp;_brightness, 200, updateBrightnessContrast);</div><div class="line">    <a class="code" href="../../d7/dfc/group__highgui.html#gaf78d2155d30b728fc413803745b67a9b">createTrackbar</a>(<span class="stringliteral">&quot;contrast&quot;</span>, <span class="stringliteral">&quot;image&quot;</span>, &amp;_contrast, 200, updateBrightnessContrast);</div><div class="line"></div><div class="line">    updateBrightnessContrast(0, 0);</div><div class="line">    <a name="a27"></a><a class="code" href="../../d7/dfc/group__highgui.html#ga5628525ad33f52eab17feebcfba38bd7">waitKey</a>();</div><div class="line"></div><div class="line">    <span class="keywordflow">return</span> 0;</div><div class="line">}</div></div><!-- fragment --> </div><!-- contents -->
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